A technique for recovering Doppler line profiles from fabry-perot interferometer fringes of very low intensity

A technique for recovering doppler line profiles from Fabry-Perot interferometer fringes of very low intensity is described. The technique is based on a fourier decomposition of the data and a subsequent nonlinear least squares fit of the low order fourier coefficients to the fourier decomposition of an ideal instrument function. The ideal instrument function is expressed by the convolution of various instrument broadening functions and includes a parametric representation of the actual instrument. The method for recovering doppler temperature, emission line intensity, and mass motion of the emitting molecules is described. A theoretical analysis of errors for doppler temperature and emission line intensity is made for a statistical noise distribution superimposed upon a fringe profile of very low intensity. These errors are related to the emission line intensity, number of data points per fringe, background continuum level, and instrument parameters. As a specific example, the errors in retrieving the doppler temperature from the 6300-A atomic oxygen emission line OI((1)D - (3)P) in the nightglow are determined for the 15-cm Fabry-Perot interferometer at the University of Michigan Airglow Observatory.